def openapi(self) -> Dict[str, Any]:
        """
        Generate the OpenAPI schema of the application. This is called by FastAPI
        internally.

        The first time it is called it stores the result in the attribute
        `app.openapi_schema`, and next times it is called, it just returns that same
        result. To avoid the cost of generating the schema every time.

            # By being a new field, no inheritance will be passed as is. A new model
            # will always be created.
            # TODO: remove when deprecating Pydantic v1
            self.secure_cloned_response_field: Optional[
                ModelField
            ] = create_cloned_field(self.response_field)
        else:
            self.response_field = None  # type: ignore